I can't make up my mind.
The biggest "selling" points in iOS 6, for me anyway, is:
1. The free, fast Panoramic Camera mode
2. Free, Turn-by-Turn Navigation
3. Upgraded Siri stuff (which may be available still on iOS5 5.1. for all we know).
However, with my jailbroken 4S, I'll be giving up all my free Jailbreak Tweaks:
1. SBsettings
2. KillBackground
3. 5 Column Dock
4. 5 Column Springboard
5. LiveClock
6. NetMeter Widget
7. BatteryInfo Lite
These are pretty damn important tweaks to me. They make my phone work and feel much more efficiently, IMO. But they are all FREE, so it's not like I'm throwing money away upgrading to iOS 6.
Still, WHO KNOWS when iOS 6 will be Jailbroken. SBSetttings alone is easily the biggest feature iOS 6 doesn't have and one that I use every single day for quick-access to settings.
Such a tough decision... I can't decide.